The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.
Heating, ventilation and/or air conditioning (“HVAC”) systems commonly employ blower systems for moving air. These blower systems typically include a fan (such as a squirrel cage fan), an electric motor for driving rotation of the fan, and a controller for the electric motor. In some systems, the controller receives an air flow demand from a system controller, such as a thermostat, and converts the air flow demand into a motor torque demand. The controller then produces drive signals for the motor that are intended to produce the demanded torque so as to produce the demanded air flow. Thus, to accurately produce the demanded air flow in such systems, the controller must accurately convert the air flow demand into a corresponding torque demand.
A variety of schemes are known for converting air flow demands into torque demands. For example, U.S. Pat. No. 4,978,896 provides a multiple slope algorithm for maintaining desired airflow rate over a range of static pressures. In particular, different torque demand equations with different slopes are used depending upon the speed of the motor. At low speeds, torque is directly proportional to the square of the desired airflow rate. At speeds above the maximum operating speed, torque is reduced using a different equation, etc.
U.S. Pat. No. 5,447,414 presents another method for producing a torque demand from an airflow demand in accordance with the formula: Torque=K1*S*CFM+K2*S+K3*CFM+K4, where S is the speed of the motor, CFM is the demanded airflow, and K1, K2, K3 and K4 are coefficients relating to a particular blower system.
Most known methods require data to be collected in some form to establish a relation between torque, speed and airflow. The collected torque, speed and airflow data is then fitted, either linearly or using multiple slope methods as in U.S. Pat. No. 4,978,896, or by using a torque equation as in U.S. Pat. No. 5,447,414, to find the coefficients K1, K2, K3 and K4.
Although these known schemes are suitable for certain applications, improvements are needed to minimize prediction errors when converting an air flow demand (or another fluid flow demand) into a torque demand.